> > > Ideally, NodeB ought to "catch up" when it joins the cluster by
> > > syncing the content in the disk page stores at that time.  I think
> > > it's a flaw we should track and fix at some point.
> > >
> > > Nice job, Matej!
> >
Well, I'm afraid as Igor said this is not possible to do without
having container specific code. So when currently a new node catch up
it only gets the last page for each pagemap.

> On Wed, 2008-01-09 at 22:35 -0800, Igor Vaynberg wrote:
> > this cant be accomplished transparently. we would need our own network
> > connection, node discovery, blah blah blah. loses a bit of appeal.
Yeah. This is actually not that difficult to do, there are frameworks
such as tribes that do this quite nicely. The main problem is that we
don't know the topology. We don't know which node is backed by which
node, so we would do lot of unnecearry copying. I don't see any easy
way to implement this.

> I'm intending to stir the pot a bit, but why are we kicking this further?  
> Igor is absolutely right..  For something simple, currently in the linux 
> kernel try
>
> drbd [1]
>
> 1) Nodes can catch up/sync
> 2) It'll be faster than anything you can do inside java
> 3) transparent to the application
> 4) debugged and proven to work inside a production env
> 5) means you can revert your changes and we don't have to worry/test anything
> -----------------------------------
>
> To be honest you may be on the right path long term and I don't currently 
> have a better suggestion, but we are really reinventing the wheel here which 
> leads me to be highly cautious.

Reinventing the wheels? How does drbd handle the topology. Does it
know which nodes are backed by which node? Usually in more
sophisticated environment each node in cluster is backed by one other
node forming a ring and the container can be in charge of forming the
topology. How does drbd handle scenario like that?

-Matej

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